Tensor Polarization and Spectral Properties of Vector Meson in QCD Medium

We calculate the tensor polarization and the resulted spin alignment of a generic vector meson in local equilibrium up to the first order in hydrodynamic gradients using thermal field theory with dissipative effects incorporated. Several new contributions, including a novel shear-induced tensor polarization (SITP), are discovered and turn out sensitive to the in-medium spectral properties of the vector mesons. The phenomenological study reveals that these contributions, especially SITP, could generate substantial spin alignment in heavy-ion collisions, and potentially helps us to understand the large spin alignment observed in experiments.